This invention relates to a necking-out tool for forming projecting cylindrical nipples ("necks") on the circumferential wall of a pipe, container or the like, having a screw plug with a hook-shaped forming head, a thrust sleeve provided with a coaxial downholder flange for cooperation with the forming head and the screw plug and a hollow cylindrical interior corresponding to the contour of the forming head of the reception of the formed neck.
When such a tool is used, a hole is first drilled into the cylindrical hollow body that is to be provided with the nipple ("neck"), the diameter of the hole just permitting the forming head of the tool to be passed through. For this purpose, the forming head is turned far enough out of the thrust sleeve to enable it to be manipulated through the hole by taking advantage of an oblique slot cut into the head. The tool is then re-erected into a radial position in relation to the pipe axis and the forming head is retracted into the thrust sleeve by rotating the screw plug. This operation causes the material of the hollow body to be plastically deformed into the shape of a projecting edge having an external diameter corresponding to the internal diameter of the thrust sleeve. During this forming process, the thrust sleeve bears on the hollow body which takes up the reactive force. A tool of this type and the manner in which it functions is described in U.S. Pat. No. 3,882,707.
The process of forming the neck calls for the application of fairly considerable forces which in magnitude depend on the nature of the material and particularly on the dimensions of the pipe and of the nipple which is to be formed on the pipe. The production of large diameter nipples on pipes which have thick walls requires the generation of forces rather beyond the physical strength of a fitter without special aids. The effort must be applied to the screw plug in the form of a torque. Apart from the purely deforming forces the frictional forces between the forming tool and the material that is to be deformed, as well as the friction between the threads of the screw plug and the thrust sleeve must also be overcome. The torque is usually applied to the screw plug by means of a lever, preferably a ratchet wrench. In view of the space needed for manipulation, it is naturally impossible to arbitrarily extend the length of the lever arm in order to improve the mechanical advantage.